Aspects of MOF chemistry related to the nuclear energy field: chemistry of actinides carboxylates and use of MOF for the capture of radioactive elements

International audienceCoordination polymers are built up from the association of metallic centers with organic (e.g. O- or N-donor) ligands. For the last two decades, this assembling concept has been applied for the generation of the so-called Metal-Organic Frameworks (MOFs), which have been investigated for many potential applications in various domains like catalysis, gas storage, optics or medicine. Recently, the strategy has been successfully used with the particular case of actinides (An) [1]. Most of the studies have mainly reported the synthesis of such solid open-framework networks bearing U(VI) or Th(IV), while trans-uranium elements have been much less studied due to their high radiotoxicity and limited amount of source material. Among the possible oxidation states of An, the tetravalent state has been investigated less actively and large polyoxo clusters have been isolated for U or Pu. In contrast, there is not much data concerning Np(IV) compounds.In the present talk, we firstly present the formation of several series of uranyl-organic frameworks associated to poly-carboxylate linkers, by following the pH variation parameter of the reaction medium, related to the hydrolysis rate. This strategy was then applied to actinides(IV), which are known to exhibit a strong affinity for the hydrolysis reaction in order to form inorganic entities with high nuclearities. In this approach, the control of water content in reaction media containing organic solvent will be investigated in different chemical systems with Th(IV) and U(IV) [2] in the presence of dicarboxylic acids molecules (typically terephthalic acid), and was then extended to Np(IV) for some cases [3]. The structural descriptions of the different coordination polymers will point out the nuclear variation of the inorganic bricks from mononuclear [AnO 9] up to hexanuclear entities [An 6O 8]. The latter is observed in the well-known series of UIO-66(Zr) MOF compounds.The second strategy was to use prototypical MOFs (MIL-n, UiO-66, ZIF-8) for the capture of radioactive molecules generated during a nuclear accident like iodine derivatives (I 2, CH 3I) or actinides (U, Th) [4]. In each case, the MOF compounds exhibit very high sorption capacities, modulated by the size of the pores and the functionalization of the framework. The resistance of MOF compounds under irradiative conditions (gamma ray irradiation) will be also discussed [5]